Thermal stabilization of concentrated alkyllead compounds



United States Patent 3,038,918 THERMAL STABlLlZATlON 0F CON CENTRATEE) ALKYLLEAD COMPGUNDS Shirl E. Cook and Hymin Shapiro, Baton Rouge, La., assignors to Ethyl Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed July 13, 1960, Ser. No. 42,466

Claims. (Cl. 260-437) This invention relates to marked improvements in the thermal stabilization of alkyllead compounds.

It is well known that pure or concentrated alkyllead compounds are susceptible to thermal decomposition when subjected to elevated temperatures in excess of about 100 C. In U.S. 2,660,591-2,660,596, inclusive, there are described a series of inventions relating to the thermal stabilization of alkyllead compounds during various manufacturing and related operations. These prior inventions primarily related to the stabilization of tetraethyllead during the separation step in its manufacture wherein the tetraethyllead is distilled (100 C.) from the reaction products accompanying its synthesis. This objective was accomplished by using a small amount of a chemical compound described in those patents as a thermal stabilizer. Hence, the incorporation with an alkyllead compound of a thermal stabilizer resulted in the substantial inhibition, delay, or retardation of the inception of pronounced thermal deterioration even when the resultant composition Was subjected to elevated temperature conditions above 100 C.

In accomplishing the foregoing objective it was discovered that various types of thermal stabilizer compounds had considerable effectiveness in inhibiting the arrival of the point at which pronounced thermal deterioration set in. These thermal stabilizer compounds were characterized by having a boiling point at least as high as 1 C. at atmosphere pressure and examples of these compounds are set forth in the above-referred-to patents.

Unfortunately, however, it has been discovered that notwithstanding the copresence of a conventional thermal stabilizer in an alkyllead compound, once the pronounced thermal decomposition sets in, it occurs with considerable force and violence. In short, even though a heretoforediscovered thermal stabilizer is used, the thermal decomposition rate of the composition is exceedingly rapid once the inhibition or induction period provided by the stabilizer has been traversed. The ultimate decomposition is of explosive magnitude. From a safety standpoint it is very desirable to reduce the speed of the thermal decomposition reactions of alkyllead compounds so as to reduce the violence and explosive force of the catastrophic thermal decomposition once it sets in. The need for such an additional safety factor, long extant in the art, has now been fulfilled.

Accordingly, an object of this invention is to fulfill the foregoing need. Another object is to provide marked improvements in the art of alkyllead thermal stabilization at highly elevated temperatures. A further object is to provide alkyllead compositions which not only have substantial stability even at temperatures as high as 195 C. but which possess in addition asafety factor such that upon eventual thermal decomposition the violence and force of the normally explosive reactions are substantially minimized. Still another object is to provide methods for accomplishing these results. Other impor: tant objects of this invention will be apparent from the ensuing description.

In accomplishing the foregoing objectives of this invention trihydrocarbyl esters of orthophosphoric acid in which each ester group contains from 1 to about 10 carbon atoms are used in conjunction with heretofore known thermal stabilizer compounds as additive mixtures to alkyllead compounds. In this invention very effective use can be made of any of a large number of thermal stabilizer compounds having the property of inhibiting the decomposition of an alkyllead compound when subjected to elevated temperature conditions above C., such compound having a boiling point of at least as high as 1 C. at atmospheric pressure. For further details concerning such thermal stabilizer compounds, the methods by which they are employed, the effects which they produce, and the kind of materials involved, reference should be had, for example, to U.S. 2,660,591- 2,660,596, inclusive, all disclosures of which are hereby incorporated herein by the foregoing reference.

By using the above-described phosphate esters in conjunction with conventional thermal stabilizers the need described hereinabove has been fulfilled. Extensive experimental work has shown that the copresence of these particular esters with thermal stabilizer compounds causes a very marked reduction in the rate of thermal decomposition reactions once the thermal stabilizer ingredient is no longer capable of preventing the onset of the decomposition. It is seen, therefore, that this invention not only enables the art to enjoy the safety factor of prolonged inhibition or retardation of the onset of thermal decomposition (the chief advantage of prior inventions in this art) but to reap the additional benefit, inter alia, of marked diminution in the force and violence of the decomposition itself once it finally does occur.

A particularly preferred class of thermal stabilizer compounds for use in the practice of this invention are those which, in addition to having a boiling point at least as high as 1 C. at atmospheric pressure are organic compounds characterized by containing in the molecule carbon, hydrogen and up to two other elements selected from the group consisting of oxygen, nitrogen, sulphur, iodine and aluminum. Numerous examples of these compounds are presented, for instance, in U.S. 2,660,S9l- 2,660,596, inclusive. These particularly preferred ma terials cooperate with the phosphate esters in such ideal fashion that there results an extremely large reduction in the rate of the alkyllead thermal decomposition reaction.

Another especially preferred category of thermal stabilizer compounds used in conjunction with the foregoing phosphate esters is composed of the following:

(1) Fused ring aromatic hydrocarbons, e.g. those containing from about 9 to about 24 carbon atoms in the molecule;

(2) Nitroalkanes, e.g. those containing from 1 to about 12 carbon atoms in the molecule;

(3) Alkyl nitrites, e.g. those containing from 2 to about 18 carbon atoms in the molecule;

(4) Ol-efinically unsaturated aliphatic monocarboxylic acids, e.g. those containing from 3 to about 24 carbon atoms and from 1 to about 3 olefinic double bonds in the molecule;

(5) Polyiodoalkanes, e.g. those containing from 1 to about 8 carbon atoms and from 2 to about 4 iodine atoms in the molecule;

(6) Perhaloalkanes, e.g. those containing from 2 to about 4 carbon atoms in the molecule and in which the halogen is chlorine, bromine, or both; and

(7) Olefinic hydrocarbons, e.g. those containing from 4 to about 24 carbon atoms in the molecule and in which the [boiling point is at least 1 C. at atmospheric pressure.

The use of the foregoing especially preferred thermal stabilizers in conjunction with the phosphate esters pursuant to this invention results in a dual advantage. In the first place, the rate of the thermal decomposition reaction is markedly reduced by such combinations.

Moreover, the time required for the inception of this thermal decomposition is significantly lengthened over that required when only the thermal stabilizer is used even though the alkyllead composition containing the combination of the preferred thermal stabilizer and the phosphate is continuously subjected to temperatures as high as 195 C.

Preferred among the phosphate esters used pursuant to this invention are those having the formula R2 wherein R R and R are radicals selected from the group consisting of methyl, phenyl, tolyl and xylyl. Not only are these particular preferred phosphates extremely effective in sharply reducing the rate of alkyllead thermal decomposition when used in conjunction with thermal stabilizer compounds, but they exert profound beneficial effects upon the gasoline fuel compositions in which the 'alkyl'lead compositions are, for the most part, ultimately employed.

For illustrations of the compositions and methods of this invention and demonstrations of the excellent results provided thereby reference should be had to the following specific examples in which all percentages are by weight. The percentages for the additives (i.e. thermal stabilizers and phosphates) are all based on the weight of the alkyllead compound.

EXAMPLE I .With pure tetraethyllead-Le. halogen scavenger-free tetraethylleadwere blended 11.5 percent of an approximately equimolar mixture of phenyl dimethyl phosphate and methyl diphenyl phosphate (a small amount of triphenyl phosphate was also present in this mixture) and 5 percent of alpha-methyl naphthalene. The resultant composition was maintained at 195 C. until thermal decomposition occurred and the rate of the thermal decomposition reaction compared with the rate obtained on the corresponding composition which did not contain the phosphate ingredient. It was found that the decomposition rate of the phosphate-containing mixture was less than the rate of the corresponding phosphorus-free system. In other words, the copresence of the phosphate resulted in more than a 40-fold reduction in thermal decomposition rate.

EXAMPLE it With pure tetraethyllead was admixed 5 percent of a commercially available mixture of fused ring aromatic hydrocarbons. This mixture was shown by infrared and ultra-violet analyses to contain a significant quantity of dimethyl naphthalene isomers as well as some higher polynuclear aromatic compounds. This mixture has the following distillation temperature profile:

Distillation C.:

Initial 254 90% 307 Final 323 When tested as in Example I it was found that the copresence of approximately 11 percent of tributyl phosphate caused a more than a 15-fold reduction in thermal decomposition rate as compared with the corresponding phosphorus-free system.

EXAMPLE III The rate of decomposition (induced by heating at 195 C.) of pure tetraethyllead containing 3 percent of nitroethane was found to he over 350 percent as rapid as when 8.7 percent of a mixture composed predominantly of xylyl dimethyl phosphate and a lesser amount of dixylyl methyl phosphate was used in conjunction with the tetraethyllead-nitroethane system.

EXAMPLE IV EXAMPLE V The rate of decomposition (brought on by continuous heating at 195 C.) of 5 percent of amyl nitrate with pure tetraethyllead was found to be over 650 percent as rapid as when 13.7 percent of cresyl diphenyl phosphate (commercial grade) was present in the tetraethylleadamyl nitrate system.

EXAMPLE VI The addition of 5.9 percent of t-rimethyl phosphate to pure tetraethyllead admixed with 10 percent of a20- benzene resulted in a IO-fold reduction in the rate of thermal decomposition (produced by continuous heating at 195 C.) as compared to the corresponding phosphatefree mixture.

EXAMPLE VII An almost 60-fold reduction of thermal decomposition rate was achieved in pure tetraethyllead containing 5 percent of isoamyl nitrite by admixing therewith 11.5 percent of a mixture of phenyl dimethyl phosphate and methyl diphenyl phosphate, the determinations being made by heating the respective systems at 195 C. until the decompositions occurred.

EXAMPLE VIII The procedure of Example II was repeated using 23 percent of an approximately equirnolar mixture of phenyl dimethyl phosphate and methyl diphenyl phosphate as the phosphate ingredient. It was found that the copresence of this phosphate caused a reduction in rate of thermal decomposition that was over 40 times as great as occurred in the absence of the phosphate.

EXAMPLE IX The conjoint use of 30.8 percent of commercial grade tricresyl phosphate with tetraethyllead and 5 percent of ethyl acetate caused more than a 25-fold reduction in the rate of thermal decomposition (195 C.) as compared to the rate exhibited by the corresponding phosphate-free mixture. r

EXAMPLE X As compared with tetraethyllead containing 3 percent of heptaldehyde, the copresence therewith of 8.7 percent of a mixture composed predominantly of xyly-l dimethyl phosphate and dixyly-l methyl phosphate resulted in a 15-.

fold reduction in thermal decomposition rate C. heating temperature).

EXAMPLE XI As induced by heating at 195 -C., the rated thermal decomposition of tetraethyllead containing 10 percent of 2-ethyl-l,3-hexane diol was almost 500 percent as rapid as when 11.5 percent of the phosphate mixture of E ample I was used therewith to form the corresponding :alkyllead-diol-phosphate mixture.

EXAMPLE XII The decomposition rate of tetraethyllead containing 5 percent of aluminum oleate was over 340 percent as rapid as when 13.7 percent of commercial grade cresyl diphenyl phosphate was also present in the system. The decompositions were caused by continuous exposures to 195 C.

EXAMPLE XIII EXAMPLE X! V The rate of thermal decomposition (195 C.) of tetraethyllead admixed with 15 percent of hexachloroethane was almost 350 percent as rapid as when there was also present 11.5 percent of a phenyl dimethyl phosphatemethyl diphenyl phosphate mixture.

EXAMPLE XV The addition of 15.4 percent of tricresyl phosphate to tetraethyllead containing percent of ethyl thiocyanate caused more than a 6fold reduction in thermal decomposition rate (195 C.) as compared to the rate of the same system in the absence of the phosphate.

EXAMPLE XVI The decomposition rate (195 C.) of a mixture consisting of tetraethyllead and percent of heptene-Z was over 230 percent as rapid as when there was also present 5.9 percent of trimethyl phosphate.

EXAMPLE XVII More than a 27-fold reduction in thermal decomposition rate (195 C.) resulted 'by the conjoint utilization of 13.7 percent of cresyl diphenyl phosphate with a mixture of tetraethyllead containing 3 percent of styrene as compared with the rate of the tetraethyllead-styrene mixture (no phosphate).

Other examples of the compositions of this invention which give equally good results are as follows.

EXAMPLE XVIII Tetraethyllead containing 2 percent of lepidine and percent of trixylyl phosphate.

EXAMPLE XIX A mixture composed of methyltriethyllead, 5 percent of 8-hydroxyquinaldine and 15 percent of tri-(decyl)phosphate.

EXAMPLE XX Tetramethyllead with which are admixed 4 percent of furfuryl amine and 10 percent of triethyl phosphate.

EXAMPLE XXI A mixture composed of tetraoctyllead 13 percent of furfuryl alcohol and 12 percent of triphenyl phosphate.

EXAMPLE XXII Tetraethyllead containing 1 percent of acridine and 8 percent of methyl diphenyl phosphate.

EXAMPLE XXIII With an alkyllead mixture composed of tetramethyllead (5.7 percent), methyltriethyllead (26.6 percent), dimethyldiethyllead (37.4 percent), ethyltrirnethyllead (23.8 per cent) and tetraethyllead (6.9 percent) are blended 0.5 percent of p,p--diaminodiphenylmethane and percent of tricurnenyl phosphate.

EXAMPLE XXIV Tetraisopropyllead with which are admixed 2 percent of ethanolamine and 13 percent of phenyl dioctyl phosphate.

EXAMPLE XXV A mixture composed of phenyltriethyllead, 5 percent of alpha-terpineol and 0 percent of trimethyl phosphate.

6 EXAMPLE XXVI Tetraethyllead containing 1.5 percent of aconitic acid and 8.5 percent of tricresyl phosphate.

XAMPLE XXVII An equimolar mixture of tetraethyllead and tetramethyllead with which are admixed 5 percent of o-ethylstyrene and 15 percent of phenyl dicresyl phosphate.

EXAMPLE XXVIII A mixture composed of tetraamyllead, 10 percent of stilbene and 6 percent of trimethyl phosphate.

EXAMPLE XXIX Tetraethyllead containing 15 percent of furfural and 10 percent of tributylphosphate.

EXAMPLE XXX Tetraethyllead with which are admixed 10 percent of maleic anhydride and 10 percent of tricyclohexyl phosphate.

As stated above, those especially preferred compositions of this invention containing any of the 7 types of thermal stabilizers enumerated above are characterized not only by sharply reduced thermal decomposition rates but by markedly enhanced inhibition periods prior to the onset of the decomposition reactions. This was demonstrated by conducting a series of standard thermal decomposition tests. In these tests a thermostatically controlled hot oil bath was fitted with a stirrer, thermometer, and a holder for a small reaction tube. A cc. gas buret beside the bath, and equipped with a Water-containing levelling bottle, was connected by means of rubber tubing with the reaction tube after the desired sample was introduced into this tube. After the bath was brought to a steady temperature of C., the sample-containing tube was quickly immersed in the bath and clamped with. the levelling bottle adjusted to hold the gas buret in place at a Zero reading. Then measured was the time during which the sample was held at this temperature without pronounced thermal decomposition and consequent gas evolution occurring. Another criterion of thermal stability was the length of time required for 100 milliliters of such gas to be evolved under the foregoing stringent test conditions. Thus in either instance, the longer the time, the more thermally stable was the alkyllead composition.

Exemplary of the excellent performance brought about pursuant to this invention by combining an orthophosphate ester with a fused ring aromatic hydrocarbon containing from about 9 to about 24 carbon atoms are the following data obtained using alpha-methyl naphthalene as the aromatic ingredient and an approximately equimolar mixture of phenyl dimethyl phosphate and diphenyl methyl phosphate as the phosphate ester ingredient. The data are shown in Table 1.

Table 1.Thdrmal Stability Potency of Fused Ring Aromatics Combined with Phosphate Ester Thermal Stability; Time Run Thermal Stabilizers Required for Evolution for 100 ml. of Gas, Min.

1 5% a-methyl naphthalene 11.5% phenyl 50 dimethyl phosphate-diphenyl methyl phosphate mixture. 2 10% wmethylnaphthalcne 36 3 h 23% phenyl dimethyl phosphate-diphenyl 15 methyl phosphate mixture.

Similar improvements occur when Run 1 is repeated using naphthalene,l,2,3,4 tetrahydronaphthalene, indene, anthracene, or 1,4-dibutylnaphthalene in place of the alphamethyl naphthalene.

Illustrative of the great benefits achieved by combining the phosphate with a nitroalkane containing from 1 to about 12 carbon atoms are the results shown in Table 2.

Table 2.-Thermal Stability Potency of N itroalkanes Combined with Phosphate Ester The same advantages subsist on repeating run l using 1,1- diiodoethane or 1,2-diiodopropane in place of the iodoform.

Exemplary of the striking benefits achieved by combining a phosphate ester with a perhaloalkane containing Thermal SW from 2 to about 4 carbon atoms are the data shown in bility, Time Table 6. Run Thermal Stabilizers to Reach i f gf Table 6.-Thermal Stability Potency of Perhaloalkanes e00 Combined With Phosphate Ester 1 3% Nitroethane 8.7% xylyl dimethyl 66 Thermal Staphosphate-dixylyl methyl phosphate bility;T1me mixture. Run Thermal Stabilizer to Beach 2 3% nitroethane 36 Pronounced 3 17.4% xylyl dimethyl phosphate-dixylyl 7 Decomposition,

methyl phosphate mixture. Min.

Essentially the same improvements occur on repeating 1 he ach10r0ethane+1l.5% phenyl di- 62 run 1 with nitrornethane or l-nitropropane instead of g gg g gg D nitroethane 2 n li i iii i'h ift d'h i l 3 23 p eny ime y p 05; a n y Typical of the outstanding efiectiveness achi ved by niethyi phosphate mixture. combinmg a phosphate with an alkyl nitrite contamiug from 2 to about '18 carbon atoms are the data shown in l Table 3. Use in run 1 of hexabromoethane as a replacement for I hexachloroethane gives the same improvements. Table fl l y P018116) f Alkyl N limes Illustrative of the effectiveness produced by combining Combmed Wllh Phosphate Ester 25 phosphate esters with olefinic hydrocarbons contaim g from 4 to about 24 carbon atoms are the data shown in Thermal Sta- Table 7 bility, Time Run Thermal Stablhms if fffiffi Table 7.-Thermal Stability Potency of Olefinic Decor n p i s Hydrocarbons Combined With Phosphate Ester 1 5%is0amylnltrite +11.5% phenyldimethyl 7s phosphate'diphenyl methyl phosphate Runs Thermal Stabilizers to beach mixture Pronounced 2 5% isoamyl nitrite 21 Decomposition 3 23% phenyl dimethyl phosphate-diphenyl 1 Min methyl phosphate mixture.

1 3% styrene-{43.7% eresyl dlphenyl phos- 103 Repetition of run 1 with butyl nitrite and Z-ethylhexyl 2 ggggj 15 nitrite instead if isoamyl nitrite gives the same advantages. 311:: 27.4% aesyraigmiyi51355115t5ii2112231131 8 Representative of the benefits produced by combining a phosphate with an olefinically unsaturated aliphatic monocarboxylic acid containing from 3 to about 24 carbon atoms and from about 1 to about 3 double bonds are the data shown in Table 4.

Table 4.--Thermal Stability Potency of Olefinically Unsaturated Monocarboxylic Acids Combined With Phosphate Ester Thermal Stability, Time Run Thermal Stabilizers to Reach Pronounced Decomposition, Min.

10% oleic acid +59% trimethyl phosphate- 26 10% oleic acid 10 11.8% trimethyl phosphate 1 Substitution of linoleic acid or linolenic acid for the oleic acid in run 1 gives very similar results.

The significant benefits achieved by combining a phosphate ester with a polyiodoalkane containing from 1 to about 8 carbon atoms and from 2 to about 4 iodine atoms is typified by the data shown in Table 5.

Table 5.-Thermal Stability Potency of Polyiodoalkanes Combined With Phosphate Ester Heptene-Z, octene1, and propenyl benzene all give similar results when used in place of styrene in run 1.

Additional thermal stabilizers which can be effectively used in the practice of this invention include hydrocarbyl ethers possessing in the molecule at least 1 aromatic hydrocarbon group and from 1 to 2 other oxygen atoms (e.g. the dibenzyl ether of hydroquinone, naphthol methyl ether, etc); aralkoxy phenols (e.g. 4(phenylmethoxy)- phenol, 4-(phenylmethoxy)-2,6-xylenol, etc.); dialkyl 'benzenes where the total number of carbon atoms in the alkyl groups is at least 4 (e.g. diethyl benzene, cymene, etc); aryl canbinols containing 7-30 carbon atoms (e.g. triphenyl carbinol, di-l-naphthyl carbinol, etc); saturated aliphatic aldehyles (e.g. heptaldehyde, etc.); saturated aliphatic monocarboxylic acids having up to 12 carbon at ms (e.g. formic acid, acetate acid, naphthenic acid, lauric acid, etc); alkyl acetates (e.g. amyl acetate, tert-butyl acetate, etc.); the cresols; tert-alkyl hydroperoxides; tert-aralkyl hydroperoxides; di-tert-alkyl peroxides; diarayl peroxides; eugenol; isoeugenol; vanillin; aromatic monocarboxylic acids (e.g. benzoic acid, etc.) thiovanic acid and esters thereof; aromatic sulfonic acids (e.g. p-toluene sulfonic acid, benzene sulfonic acid, etc.); azo phenols (e.g. benzene azo resorcinol, alpha-naphthalene azo phenol, beta-naphthalene azo resorcinol, beta-naphthalene azo resorcinol, p-nitro benzene azo resorcinol, m-nitro benzene azo resorcinol, etc.); monoamides (e.g. formamide, benzamide, etc.); and others.

The thermal stabilizer-orthophosphate ester combinations of this invention have such efiectiveness that even minute quantities thereof produce a detectable improvement in the thermal stability characteristics of scavengerfree alkyllead compounds, even at C. However, it is generally preferable to employ from about 0.5 to about 45 percent by weight of the thermal stabilizer ingredient and from about 2 to about 50 percent by weight of the phosphate ester ingredient in order to achieve the maximum benefits characteristic of this invention. In other words, for every 100 parts by weight of alkyllead compound one should use from about 0.5 to about 45 parts by weight of the thermal stabilizer and from about 2 to about 50 parts by weight of the phosphate ester. As a general rule, the concentration of the phosphate should be directly proportional to its molecular weight.

It is desirable in those instances where the thermal stabiliZer-orthophosphate ester combinations are solids at ordinary temperatures to use an appropriate diluent for these materials. Suitable materials for this purpose include liquid hydrocarbons, alcohols, ketones and the like. It is seen, therefore, that in some cases additional benefits are to be derived by using mixtures of known thermal stabilizers in conjunction with the phosphate ester, at least one of the thermal stabilizers being a liquid material such as dipentene, cyclohexene, furfuryl alcohol, or furfuryl amine, which will serve the dual function of contributing improved solubility characteristics upon the resultant mixture as well as conferring thereupon its own thermal stabilizing capacity.

Methods for the preparation of the ingredients used in the practice of this invention are well known to those skilled in the art. In fact many of the foregoing ingredients are readily available as articles of commerce.

This invention is useful in stabilizing alkyllead compounds in which at least one valence of the lead is satisfied by an alkyl radical. For example tetraethyllead, tetramethyllead, tetrapropyllead, dirnethyldiethyllead, triethylphenyllead, and triethyllead bromide can be successfully stabilized against thermal decomposition at 180- 195 C. by incorporating therewith a thermal stabilizerphosphate mixture of this invention.

What is claimed is: r

1. In a composition consisting essentially of an alkyllead compound and a thermal stabilizer compound having a boiling point at least as high as 1 C. at atmospheric pressure and the property of inhibiting the decomposition of the alkyllead when subjected to elevated temperature conditions from about 100 C. to about 195 C., the improvement by which (a) said thermal stabilizer compound is selected from the group consisting of (1) fused ring aromatic hydrocarbons containing from about 9 to about 24 carbon atoms in the molecule; (2) nitroalkanes containing from 1 to about 12 carbon atoms in the molecule; (3) alkyl nitrites containing from 2 to about 18 carbon atoms in the molecule; (4) olefinically unsaturated aliphatic monocarboxylic acids containing from 3 to about 24 carbon atoms and from 1 to about 3 olefinic double bonds in the molecule; (5) polyiodoalkanes containing from 1 to about 8 carbon atoms and from 2 to about 4 iodine atoms in the molecule; (6) perhaloalkanes containing from 2 to about 4 carbon atoms in the molecule and in which the halogen is taken from the group consisting of chlorine and bromine; and (7) olefinic hydrocarbons containing from 4 to about 24 carbon atoms in the molecule; and (b) there is copresent with said thermal stabilizer compound a trihydrocarbyl ester of orthophosphoric acid in which each ester group contains up to about carbon atoms, said ester having the general formula wherein R R and R are radicals selected from the group consisting of methyl, phenyl, tolyl and Xylyl.

3. The composition of claim 1 wherein said alkyllead compound is tetraethyllead.

4. The composition of claim 1 wherein said alkyllead compound is tetramethyllead.

5. In the method of inhibiting the decomposition of a concentrated alkyllead compound which method comprises incorporating therewith a thermal stabilizer compound having the property of inhibiting the decomposition of the alkyllead compound when subjected to elevated temperature conditions from about C. to about C. said thermal stabilizer compound having a boiling point at least as high as 1 C. at atmospheric pressure, the improvement by which (a) said compound is selected from the group consisting of (1) fused ring aromatic hydrocarbons containing from about 9 to about 24 atoms in the molecule; (2) nitroalkanes containing from 1 to about 12 carbon atoms in the molecule; (3) alkyl nitrites containing from 2 to about 18 carbon atoms in the molecule; (4) olefinically unsaturated aliphatic monocarboxylic acids containing from 3 to about 24 carbon atoms and from 1 to about 3 olefinic double bonds in the molecule; (5) polyiodoalkanes containing from 1 to about 8 carbon atoms and from 2 to about 4 iodine atoms in the molecule; (6) perhaloalkanes containing from 2 to about 4 carbon atoms in the molecule and in which the halogen is taken from the group consisting of chlorine and bromine; and (7) olefinic hydrocarbons containing from 4 to about 24 carbon atoms in the molecule; and (b) there is ce-incorporated with said compound a trihydrocarbyl ester of orthophosphoric acid in which each ester group contains up to about 10 carbon atoms, said ester having the general formula wherein R R and R are radicals selected from the group consisting of alkyl, cycloalkyl, aryl, and alkaryl.

6. The method of claim 5 wherein said ester has the general formula wherein R R and R are radicals selected from the group consisting of methyl, phenyl, tolyl, and xylyl.

9. The method of claim 5 wherein said thermal stabilizer compound is at least one fused ring aromatic hydrocarbon containing from about 9 to about 24 carbon atoms in the molecule.

10. The method of claim 5 wherein said thermal stabilizer compound is at least one fused ring aromatic hydrowherein R R and R are radicals selected from the group consisting of methyl, phenyl, tolyl, and Xylyl.

References Cited in the file of this patent 7 UNITED STATES PATENTS Calingaert et a1. Nov. Calingaert et a1 Nov. Calingaert et a1 Nov. Calingaert et a1. Nov. Calingaert et al Nov. Calingaert et a1. Nov. Pagliarini Aug. Shepherd Dec. 

1. IN A COMPOSITION CONSISTING ESSENTIALLY OF AN ALKYLLEAD COMPOUND AND A THERMAL STABILIZER COMPOUND HAVING A BOILING POINT AT LEAST AS HIGH AS 1*C, AT ATMOSPHERIC PRESSURE AND THE PROPERTY OF INHIBITING THE DECOMPOSITION OF THE ALKYLLEAD WHEN SUBJECTED TO ELEVATED TEMPERATURE CONDITIONS FROM ABOUT 100*C, TO ABOUT 195*C, THE IMPROVEMENT FROM WHICH (A) SAID THERMAL STABILIZER COMPOUND IS SELECTED FROM THE GROUP CONSISTING OF (1) FUSED RING AROMATIC HYDROCARBONS CONTAINING FROM ABOUT 9 TO ABOUT 24 CARBON ATOMS IN THE MOLECULE; (2) NITROALKANES CONTAINING FROM 1 TO ABOUT 12 CARBON ATOMS IN THE MOLECULE; (3) ALKYL NITRITES CONTAINING FROM 2 TO ABOUT 18 CARBON ATOMS IN THE MOLECULE; (4) OLEFINICALLY UNSATURATED ALIPHATIC MONOCARBOXYLIC ACIDS CONSTAINING FROM 3 TO ABOUT 24 CARBON ATOMS AND FROM 1 TO ABOUT 3 OLEFINIC DOUBLE BONDS IN THE MOLECULE; (5) POLYIODOALKANES CONTAINING FROM 1 TO ABOUT 8 CARBON ATOMS AND FROM 2 TO ABOUT 4 IODINE ATOMS IN THE MOLECULE; (6) PERHALOALKANES CONTAINING FROM 2 TO ABOUT 4 CARBON ATOMS IN THE MOLECULE AND IN WHICH THE HALOGEN IS TAKEN FROM THE GROUP CONSISTING OF CHLORINE AND BROMINE; AND (7) OLEFINIC HYDROCARBONS CONTAINING FROM 4 TO ABOUT 24 CARBON ATOMS IN THE MOLECULE; AND (B) THERE IS COPRESENT WITH SAID THERMAL STABILIZER COMPOUND A TRIHYDROCARBYL ESTER OF ORTHOPHOSPHORIC ACID IN WHICH EACH ESTER GROUP CONTAINS UP TO ABOUT 10 CARBON ATOMS, SAIS ESTER HAVING THE GENERAL FORMULA 